1. Field of the Invention
The present invention relates to a multimode frequency synthesizer using a phase-locked loop (PLL) that can be installed in 802.11 b/g HYPERLAN (HIgh PErformance Radio LAN), Dedicated Short Range Communications (DSRC), 802.11 a, and Ultra Wide Band (UWB) systems having applications in a 2˜9 GHz frequency band.
2. Discussion of Related Art
Recently, as mobile communication services are becoming increasingly widespread, available frequency bands are becoming saturated, and several terminals are required to enjoy various mobile communication services. As a result, developers all over the world are working on a reconfigurable mobile communication system capable of reconfiguring mobile communication services in software and enabling access to various mobile communication services using one terminal regardless of encoding and decoding method. To access necessary services using one terminal regardless of time and place, a wide-band Radio Frequency (RF) transceiver of a mobile communication system is required.
To manufacture the multiband multimode RF transceiver, a wide-band Local Oscillator (LO) are required. FIG. 8 illustrates a conventional wide-band frequency synthesizer including a phase frequency detector 20, a charge pump 30, a low pass filter 40, a voltage-controlled oscillator 50, and a variable frequency divider 70.
To satisfy requirements that vary depending on field of application when the frequency synthesizer for multiband multimode is manufactured, there should be a certain amount of flexibility in selecting components of the frequency synthesizer. However, use of a voltage-controlled oscillator, a high speed prescaler, a charge pump, and a loop filter diminishes flexibility in the construction of the frequency synthesizer. Therefore, a plurality of voltage-controlled oscillators and phase-locked loop (PLL) loops are used to manufacture the multiband frequency synthesizer. However, using a plurality of voltage-controlled oscillators and PLL loops results in increased chip size and power consumption.